In addition to a large power circuit, it is known to use a small auxiliary power supply unit in a switched-mode power supply, especially for a charging device; the auxiliary power supply unit generates multiple output voltages in order to supply various switching circuits or switching controllers for controlling or regulating the power circuit and possibly additional consumers. For example, such switching circuits or consumers can be a primary-side switching controller or a microprocessor on the secondary side of a switched-mode power supply transformer.
To satisfy energy savings standards, it is necessary for the switched-mode power supply to operate at a considerably reduced power in a further operating mode, for instance an energy-saving or standby operation, in comparison with a first operating mode, e.g., a regular or normal operation. To do so, the power circuit of the switched-mode power supply can be switched off. This is currently accomplished with the aid of a switching circuit logic, which separates the individual output voltages of the auxiliary power supply unit from the switching circuits or switching controllers.